Congestive heart failure is the loss of pumping power of the heart, resulting in the inability to deliver enough blood to meet the demands of peripheral tissues. Congestive heart failure (CHF) may cause weakness, loss of breath, and build up of fluids in the lungs and other body tissues.
CHF is usually a chronic, long term condition, but can occur suddenly. It may affect the left heart, right heart or both sides of the heart. Heart failure has a variety of causes, primarily ischemic heart disease. The deterioration of the muscles of the heart caused by ischemic heart disease result in an enlargement of the heart and reduced contractility. The reduced contractility decreases the cardiac output of blood and typically results in an increased heart rate. Cardiac conduction path block may also occur in the enlarged heart tissue, causing the signals that control the heart rhythm to travel more slowly through the enlarged heart tissue. For example, if CHF affects the left ventricle, signals that control the left ventricular contraction are delayed, and the left and right ventricles do not contract simultaneously. Non-simultaneous contractions of the left and right ventricles decrease the pumping efficiency of the heart.
CHF may be treated by medication and/or by cardiac pacing therapy. Pacing therapy to promote synchronization of heart chamber contractions for improved cardiac function is generally referred to as cardiac resynchronization therapy (CRT). Some cardiac pacemakers are capable of delivering CRT by pacing multiple heart chambers. Pacing pulses are delivered to the heart chambers in a sequence that causes the heart chambers to contract with enhanced synchrony, increasing the pumping power of the heart and delivering more blood to the peripheral tissues of the body. In the case of dysynchrony of right and left ventricular contractions, a CRT pacing may be used to resynchronize the left and right ventricles. Successful pacing of the left ventricle is critical to achieve the benefit of CRT. Bi-atrial pacing or pacing of all four heart chambers may also be used.
Pacing therapy is delivered by pacing one or more heart chambers using pacing delays that control the timing and sequence of the pacing pulses. Appropriate specification of these pacing delays is desirable to achieve improvement of cardiac function through enhanced synchrony. For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading the present specification, there is a need in the art for methods and systems that provide for determination of delays used for CRT pacing. The present invention fulfills these and other needs.